Al, Can we merge this patch, if there are no further comments?
Thanks, Sahitya. On Thu, Jan 03, 2019 at 04:48:15PM +0530, Sahitya Tummala wrote: > In the vfs_statx() context, during path lookup, the dentry gets > added to sd->s_dentry via configfs_attach_attr(). In the end, > vfs_statx() kills the dentry by calling path_put(), which invokes > configfs_d_iput(). Ideally, this dentry must be removed from > sd->s_dentry but it doesn't if the sd->s_count >= 3. As a result, > sd->s_dentry is holding reference to a stale dentry pointer whose > memory is already freed up. This results in use-after-free issue, > when this stale sd->s_dentry is accessed later in > configfs_readdir() path. > > This issue can be easily reproduced, by running the LTP test case - > sh fs_racer_file_list.sh /config > (https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/fs/racer/fs_racer_file_list.sh) > > Fixes: 76ae281f6307 ('configfs: fix race between dentry put and lookup') > Signed-off-by: Sahitya Tummala <stumm...@codeaurora.org> > --- > v2: > - update comments relevant to the code. > > fs/configfs/dir.c | 9 ++++----- > 1 file changed, 4 insertions(+), 5 deletions(-) > > diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c > index 39843fa..f113101 100644 > --- a/fs/configfs/dir.c > +++ b/fs/configfs/dir.c > @@ -58,15 +58,14 @@ static void configfs_d_iput(struct dentry * dentry, > if (sd) { > /* Coordinate with configfs_readdir */ > spin_lock(&configfs_dirent_lock); > - /* Coordinate with configfs_attach_attr where will increase > - * sd->s_count and update sd->s_dentry to new allocated one. > - * Only set sd->dentry to null when this dentry is the only > - * sd owner. > + /* > + * Set sd->s_dentry to null only when this dentry is the > + * one that is going to be killed. > * If not do so, configfs_d_iput may run just after > * configfs_attach_attr and set sd->s_dentry to null > * even it's still in use. > */ > - if (atomic_read(&sd->s_count) <= 2) > + if (sd->s_dentry == dentry) > sd->s_dentry = NULL; > > spin_unlock(&configfs_dirent_lock); > -- > Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc. > Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux > Foundation Collaborative Project. > -- -- Sent by a consultant of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
